1. Field of the Invention
This invention generally relates to a semiconductor light-emitting device and in particular to a surface emission type semiconductor light-emitting device capable of emitting light in a direction substantially perpendicular to the surface of a substrate.
2. Description of the Prior Art
A surface emission type semiconductor light-emitting device for emitting light in a direction perpendicular to the surface of a substrate is well known. Such a surface emission type semiconductor light-emitting device includes a CTJ type light-emitting device having a projection or pillar extending in a direction substantially perpendicular to the main surface of a semiconductor substrate, a Burrus type light-emitting device having an etched hole at the rear surface of a semiconductor substrate aligned in position with a light-emitting region, and a semiconductor laser having a pair of light-reflecting means at the top and bottom of an activation region.
As shown in FIG. 36, in the case of a CTJ type light-emitting device, a p-n junction is formed not only in the projection but also in the substrate so that the p-n junction in the projection extends vertically with respect to the main surface of the substrate, but the p-n junction in the substrate extends in parallel with the main surface of the substrate. Thus, when a large amount of drive current is injected, light is emitted not only from the vertical p-n junction formed in the projection, but also from the horizontal p-n junction formed in the substrate. For this reason, even if a large amount of drive current is injected, the light-emitting efficiency is not increased significantly in the vertical direction. In addition, since an activation region where recombination of holes and electrons takes place to emit light is formed inside of a columnar or pillar-like projection, heat tends to accumulate within the projection, which may adversely affect the light-emitting characteristic. In addition, because of the presence of a projection, the mechanical integrity of a CTJ type device is not so great.
As shown in FIG. 37, in the case of a Burrus type light-emitting device, a light-emitting activation layer is formed to extend in parallel with the surface of a substrate, and thus it is difficult to obtain a large light output in the direction perpendicular to the surface of the substrate. As a result, this type of light-emitting device is not suitable for a super luminescent operation and a laser oscillation. Also from the viewpoint of manufacture, since a hole must be etched in the rear surface of a substrate in positional registration with a P type diffusion region, difficulty is encountered. In addition, the hole to be etched is significantly large in size and as an example the diameter of a hole to be etched is required to be approximately ten times of the diameter of a light-emitting region, so that difficulty is encountered in obtaining an increased density when arranging a plurality of this type of light-emitting devices in the form of one or two dimensional array.
On the other hand, as shown in FIG. 38, in the case of a surface emission type semiconductor laser having a pair of light reflecting structures at the top and the bottom of an activation region, since the light reflecting structures are formed in the vicinity of the activation region, it is required to define a large hole in a substrate as a light output outlet. However, the provision of such a large hole would tend to reduce the mechanical integrity of the device as a whole. In addition, in this type of a semiconductor laser, a top electrode is arranged around the hole formed in the substrate, and the activation region cannot be formed elongated in the vertical direction, i.e., light output direction, so that current cannot be concentrated in the activation region. Thus, it cannot be hoped to obtain an enhanced current injection efficiency into the activation region. Under the condition, there remains a problem of incapability to lower the threshold current. Difficulty is also present in manufacturing this type of device because a hole must be formed in the substrate in positional alignment with a circular electrode disposed below the activation region.
Under the circumstances, there has been proposed a surface emission type light-emitting semiconductor device including a semiconductor layer formed on a substrate and formed with a hole having a p-n junction extending in parallel with the side wall of the hole and thus perpendicular to the surface of the substrate as disclosed in the U.S. patent application No. 06/946,324, filed Dec. 24, 1986, assigned to some of the assignees of the present application. In this case, since the p-n junction extends perpendicularly to the surface of the substrate, light may be output in the vertical direction.